How strong can the storm be?

Hurricane Milton, expected to make landfall on the Florida coast on October 9 or early morning of October 10, seemed to form and strengthen extremely suddenly. From a tropical storm on October 6, it strengthened into a level 5 storm on October 7 with a sustained wind speed of 298 km/h before weakening a bit on October 8, according to Live Science.

There is a speed limit to sustained wind speed, called maximum potential intensity, but it is not absolute and is governed by several factors, including ocean heat. Current calculations of the maximum potential intensity for storms often put the maximum at 322 km/h. But that could change in the next few decades as oceans warm and the climate changes. The risk of powerful storms has increased over the past 30 years, according to Kerry Emanuel, a professor emeritus of atmospheric science at MIT who developed the prediction model. 5 storms in history have had winds exceeding 309 km/h, all of which appeared after 2013.

Speed ​​limits for hurricane winds are relatively easy to calculate, according to James Kossin, a retired climate scientist at the US National Oceanic and Atmospheric Administration (NOAA) who advises the risk modeling firm Climate risk First Street. “The fuel for hurricanes is the heat they absorb from the ocean. The warmer the ocean water, the more fuel available,” Kossin said.

Other factors that help determine maximum potential intensity include atmospheric heat and cloud top temperatures (which reveal how quickly heat can move from the sea surface to the top of the storm) and wind shear (the difference between about wind speed and direction at different altitudes in the atmosphere). Too much wind shear can cause a storm to disintegrate, weaken and prevent it from reaching its full potential. A study of hurricanes between 1962 and 1992 found that only 20% of Atlantic hurricanes reached 80% or more of their maximum potential intensity, although there is evidence that more and more hurricanes are starting to get closer to their physical limit. theory, according to Emanuel.

As the ocean and atmosphere warm, storms are becoming stronger. In 2020, Kossin and colleagues reported an 8% increase in the rate of major storms per decade between 1979 and 2017. That means as the weather warms, strong and rapidly intensifying storms like Milton could become common. variable.

Tropical storms are classified according to the Saffir – Simpson scale, from level 1 (sustained wind speed of 119 km/h) to level 5 (252 km/h). This scale is incomplete because it is based on wind speed and does not include damage from storm surges or flooding, which are more dangerous than hurricane winds. The increased probability of strong storms prompted Kossin and colleague Michael Wehner at Lawrence Berkeley National Laboratory to suggest that the Saffir-Simpson scale may need to be added to level 6 to include storms with winds above 308 km/h. .

Researchers identified 5 storms that qualify for level 6 classification, including Typhoon Haiyan (2013), Typhoon Patricia (2015), Typhoon Meranti (2016), Typhoon Goni (2020) and Typhoon Surigae (2021). ). Patricia is the most intense storm in history and is also the only storm with winds over 322 km/h. The storm’s wind speed reached 345 km/h but weakened to 241 km/h when it made landfall. Wehner and Kossin considered a level 7 storm with winds above 368 km/h. But their calculations show that the risk of such a powerful storm is currently very small, so they ruled out that possibility in the study.

No one really knows for sure the maximum winds a storm could theoretically sustain if water temperatures continue to rise. The exact dynamics of the storm circulation are also not fully understood. The weakening of Hurricane Milton occurred after the replacement of the storm circulation, which occurred because a new band of thunderstorms formed around the eye of the storm, blocking moisture from the original circulation. The change dispersed Milton’s energy, increasing the storm’s size but also reducing its maximum wind speed. It is possible that at extreme wind speeds, such weakening becomes inevitable, according to Wehner.